Apparatus and methods for envelope tracking systems

Abstract

Apparatus and methods for envelope tracking systems are disclosed herein. In certain implementations, an envelope tracking system for generating a power amplifier supply voltage for a power amplifier is provided. The envelope tracking system includes a DC-to-DC converter that generates a regulated voltage from a battery voltage and controls a voltage of the regulated voltage using a low frequency feedback signal. The envelope tracking system further includes an error amplifier that generates an output current using an envelope signal and a high frequency feedback signal. The low frequency feedback signal is based on a low frequency component of the power amplifier supply voltage and the high frequency feedback signal is based on a high frequency component of the power amplifier supply voltage. The error amplifier generates the power amplifier supply voltage by adjusting the magnitude of the regulated voltage using the output current.

What is claimed is: 
     
       1. A mobile device comprising:
 a power amplifier configured to amplify a radio frequency signal and to receive power from a power amplifier supply voltage; 
 a DC-to-DC converter configured to generate a regulated voltage; 
 a high pass filter configured to generate a high pass filtered supply voltage based on high pass filtering the power amplifier supply voltage; 
 a first comparator configured to generate a high frequency envelope signal based on comparing the high pass filtered supply voltage to an envelope signal that changes in relation to an envelope of the radio frequency signal; and 
 an error amplifier configured to generate the power amplifier supply voltage by adjusting a voltage level of the regulated voltage based on the high frequency envelope signal. 
 
     
     
       2. The mobile device of  claim 1  wherein the DC-to-DC converter is configured to generate the regulated voltage based on a control voltage. 
     
     
       3. The mobile device of  claim 2  further comprising a low pass filter configured to generate a low pass filtered supply voltage based on low pass filtering the power amplifier supply voltage, and a second comparator configured to control a voltage level of the control voltage based on comparing the low pass filtered supply voltage to a reference voltage. 
     
     
       4. The mobile device of  claim 3  further comprising a reference voltage generator configured to control a voltage level of the reference voltage based on digital data received over a serial interface. 
     
     
       5. The mobile device of  claim 1  further comprising an AC coupling capacitor connected between an output of the error amplifier and the power amplifier supply voltage. 
     
     
       6. The mobile device of  claim 5  further comprising a feedback circuit connected to the output of the error amplifier and configured to generate a feedback signal, the error amplifier including a first input configured to receive the high frequency envelope signal and a second input configured to receive the feedback signal. 
     
     
       7. The mobile device of  claim 1  further comprising an inductor connected between the regulated voltage and the power amplifier supply voltage. 
     
     
       8. The mobile device of  claim 1  further comprising a transceiver configured to generate the radio frequency signal and the envelope signal. 
     
     
       9. The mobile device of  claim 1  further comprising a battery configured to provide a battery voltage to the DC-to-DC converter and to the error amplifier. 
     
     
       10. A radio frequency system comprising:
 a power management integrated circuit including a DC-to-DC converter configured to generate a regulated voltage; and 
 a power amplifier module including a power amplifier configured to amplify a radio frequency signal and to receive power from a power amplifier supply voltage, a high pass filter configured to generate a high pass filtered supply voltage based on high pass filtering the power amplifier supply voltage, a first comparator configured to generate a high frequency envelope signal based on comparing the high pass filtered supply voltage to an envelope signal that changes in relation to an envelope of the radio frequency signal, and an error amplifier configured to generate the power amplifier supply voltage by adjusting a voltage level of the regulated voltage based on the high frequency envelope signal. 
 
     
     
       11. The radio frequency system of  claim 10  wherein the DC-to-DC converter is configured to generate the regulated voltage based on a control voltage. 
     
     
       12. The radio frequency system of  claim 11  wherein the power amplifier module further includes a low pass filter configured to generate a low pass filtered supply voltage based on low pass filtering the power amplifier supply voltage, and a second comparator configured to control a voltage level of the control voltage based on comparing the low pass filtered supply voltage to a reference voltage. 
     
     
       13. The radio frequency system of  claim 12  wherein the power amplifier module further includes a serial interface configured to receive digital data and a reference voltage generator configured to control a voltage level of the reference voltage based on the digital data. 
     
     
       14. The radio frequency system of  claim 10  wherein the power amplifier module further includes an AC coupling capacitor connected between an output of the error amplifier and the power amplifier supply voltage. 
     
     
       15. The radio frequency system of  claim 14  wherein the power amplifier module further includes a feedback circuit connected to the output of the error amplifier and configured to generate a feedback signal, the error amplifier including a first input configured to receive the high frequency envelope signal and a second input configured to receive the feedback signal. 
     
     
       16. The radio frequency system of  claim 10  wherein the power amplifier module further includes an inductor connected between the regulated voltage and the power amplifier supply voltage. 
     
     
       17. A method of envelope tracking in a power amplifier system, the method comprising:
 providing a power amplifier supply voltage to a power amplifier; 
 amplifying a radio frequency signal using the power amplifier; 
 generating a regulated voltage using a DC-to-DC converter; 
 high pass filtering the power amplifier supply voltage to generate a high pass filtered supply voltage; 
 generating a high pass envelope signal based on comparing the high pass filtered supply voltage to an envelope signal that changes in relation to an envelope of the radio frequency signal; and 
 generating the power amplifier supply voltage by adjusting a voltage level of the regulated voltage based on the high frequency envelope signal using an error amplifier. 
 
     
     
       18. The method of  claim 17  further comprising providing a control voltage to the DC-to-DC converter, and generating the regulated voltage based on the control voltage. 
     
     
       19. The method of  claim 18  further comprising generating a low pass filtered supply voltage based on low pass filtering the power amplifier supply voltage, and controlling a voltage level of the control voltage based on comparing the low pass filtered supply voltage to a reference voltage. 
     
     
       20. The method of  claim 19  further comprising receiving digital data over a serial interface, and controlling a voltage level of the reference voltage based on the digital data.